(1) Field of the Invention
The present invention relates to a direct current machine, specifically to an electrically or permanent excited brushless direct current machine, and a method for manufacturing a direct current machine. Such a machine can be used as a motor, for instance for driving a bicycle, and also as a generator for energy recuperation and charging of a battery.
(2) Description of the Related Art
The known related art includes a machine disclosed in DE 199 83 946 B4. Such a machine which can be operated as a motor or a generator has two components which are orientated with respect to each other in a concentric manner, usually called rotor and stator. One of these components, namely either the rotor or the stator, has a specific number of magnets, for instance permanent magnets, which are alternatively magnetized north and south, and the respective other part has a specific number of coils which are formed by teeth around which insulated wire is wound. Between these coils there are formed respective slots. Accordingly, these slots are the gaps between adjacent teeth.
The concept whether the rotor is disposed within or outside the stator and which of both components is provided with the permanent magnets, while then the other component has the coils and slots, is particularly determined or suggested by the respective use or application of the machine. Document DE 199 83 946 B4 discloses a permanent magnet brushless direct current machine which is used as a drive for a bicycle in a wheel in the form of a hub motor, wherein the central part is disposed in a stationary manner and therefore is the stator and has the coils and the slots, respectively, and where the rotor is an outer rotor provided with permanent magnets. Fed by a rechargeable battery as a power source, the motor can be used as a drive as well as a generator for energy recuperation and charging of the battery. The drive of the machine is effected in a normal manner via a current controlled inverter having three phases.
The number of poles, i.e. magnetic poles, and the number of slots, i.e. coils, are significant features in the design of such a machine. Document DE 1 99 83 946 B4 discloses for instance a kind of machine having twenty-two poles and twenty-four slots and a further machine variant having forty-four poles and forty-eight slots.
In addition to the numbers of poles and slots, the so called pole-slot-combination, there are further features of such a machine which are decisive for its characteristics. These include the kind of winding and the manner, in which the winding of the coils is connected, i.e. the so called coil groups wiring concept. The coils can be combined in groups and the wiring can be in the form of a star connection or in the form of a delta connection.
If the winding is to be produced by a semi-automatic or all-automatic wiring machine which wiring machine is specifically designed for this purpose, such machine requires a high volume of investment. In any event, such wiring machine has to be specifically set up and programmed for each kind of winding. This requires additional investments and nonproductive time due to changing the machine set up and programming the machine.
The kind of winding and the connection of the windings, i.e. the wiring concept as well as the assembly in groups, have to be taken into account already upon design of a machine. Respective contact points, i.e. terminals, have to be planned and must be provided.
In many aspects, the present invention provides a direct current machine which, specifically in view of what is discussed above, offers a high degree of variability, as well as a corresponding method of manufacturing.